Properties of compositions comprising an ethylene-propylene-diene terpolymer (EPDM) have a direct effect on their processability for end use. Consumer applications require various adjustments of compositions comprising EPDM by adding components that are compatible with the EPDM to achieve certain properties. Rheological properties can be improved by incorporating a small amount of an EPDM with a low Mooney viscosity [ML(1+4) 125° C.], such as below 25, into a common EPDM with a relatively high Mooney viscosity [ML(1+4) 125° C.] (usually above 60) to reach a greatly increased flowability. However, such compositions usually result in relatively high cost for extensive use.
U.S. Publication No. 2011-0118404 A1 relates to natural rubber blends, methods for making the same, and articles made therefrom. The natural rubber blend includes at least one propylene copolymer containing ethylene-derived units. The natural rubber blend can further include one or more reinforcing fillers, such as carbon black. The presence of the propylene copolymer is said to improve the ozone resistance and aging properties of the natural rubber gum stock.
Xiao Sheng, “Use of specialty elastomer Vistamaxx VM1100 in an EPDM gum stock”, Rubber Industry, p 483-486, Issue 8, Vol. 54, 2007, reports the addition of certain propylene-based elastomers into EPDM gum stock containing EPDM with a Mooney viscosity [ML(1+4) 125° C.] around 80 and EPDM with a lower Mooney viscosity [ML(1+4) 125° C.] between 17 and 23 to partially replace the EPDM with the lower Mooney viscosity in an amount of no more than 20 phr relative to the total amount of both EPDM components. This replacement is said to reduce production cost while substantially maintaining heat aging and compression set properties of the original gum stock. The reference also concludes that rheological properties of the gum stock during processing, e.g., extrusion, would not be obviously changed by the propylene-based elastomer.
Given the rapidly growing demand and the relatively tight supply of EPDM raw materials with a low Mooney viscosity in recent years, it would be desirable to have an alternative to EPDM with a low Mooney viscosity that would also serve to improve flowability of compositions comprising EPDM. Applicants have found that certain polyolefin elastomers, particularly propylene-based elastomers, can provide enhanced flowability of compositions comprising EPDM with a relatively high Mooney viscosity, especially when used with an amount of, such as less than about 20 phr relative to the EPDM. It is a more cost effective way to obtain better flowability of compositions comprising EPDM without significantly compromising other properties, such as tensile strength at break and compression set, thus making the inventive compositions particularly advantageous to subsequent applications, such as extrusion.